Marine Hydrography

Numerical study on sub-mesoscale processes in the northern South China Sea

  • LUO Shihao ,
  • JING Zhiyou ,
  • QI Yiquan ,
  • XIE Qiang
Expand
  • 1. State Key Laboratory of Tropical Oceanography (South China Sea Institute of Oceanology, Chinese Academy of Sciences),Guangzhou 510301, China; 2. University of Chinese Academy of Sciences, Beijing 100049, China;

Received date: 2015-12-07

  Online published: 2016-09-22

Supported by

Foundation item: Public Science and Technology Research Funds Projects of Ocean (201305031-7); National Natural Science Foundation of China (41276022、41230962); Guangdong Province Key Laboratory for Coastal Ocean Variation and Disaster Prediction (GLOD1401)

Abstract

Recent field observations and theoretical analysis revealed the processes with the lateral scale of 0.1-10 km and time scale of O(1 day) in the mixed layer, which are termed sub-mesoscale processes. Physics at these scales are distinguished by big Rossby number (Ro) and small Richardson number (Ri). They are able to effectively extract energy from geostrophic shear through sub-mesoscale instabilities, and then forward cascade the energy to dissipation at smaller scales. Moreover, sub-mesoscale processes can play a crucial role in the transport of upper-ocean mass and energy, mesoscale variability, air-sea interaction, and upper-ocean restratification, among others. Base on the Regional Ocean Modeling System (ROMS) high-resolution (1-km) numerical experiment, we preliminarily discuss sub-mesoscale processes in the northern South China Sea (NSCS) in this paper. The results suggest that mesoscale eddies and fronts were ubiquitous in the NSCS with significant sub-mesoscale process at their edges. Analytical investigation of stability and energy in one sub-mesoscale eddy as a case study indicates that the generation of negative potential vorticity (q) resulting in symmetric instability (SI) was primarily attributable to the strong lateral buoyancy gradients adjacent to frontal vortex filament. This instability is mainly produced by the frontogenesis at the southern edge of the sub-mesoscale eddy. Moreover, the extracted energy by the SI from geostrophic shear tends to forward cascade to the turbulence at small scale, with a maximum energy extraction of 4×10-7W•kg-1 at about 20-m depth.

Cite this article

LUO Shihao , JING Zhiyou , QI Yiquan , XIE Qiang . Numerical study on sub-mesoscale processes in the northern South China Sea[J]. Journal of Tropical Oceanography, 2016 , 35(5) : 10 -19 . DOI: 10.11978/2015150

References

1 经志友, 齐义泉, 华祖林, 2008. 南海北部陆架区夏季上升流数值研究[J]. 热带海洋学报, 27(3): 1-8. JING ZHIYOU, QIYIQUAN, HUA ZULIN, 2008. Numerical study on summer upwelling over northern continental shelf of South China Sea[J]. Journal of Tropical Oceanography, 27(3): 1-8 (in Chinese).
2 刘国强, 2011. 南海北部以及吕宋海峡次级中尺度动力过程数值模拟研究[D]. 青岛: 中国科学院研究生院(海洋研究所): 131. LIU GUOQIANG, 2011. Numerical study of submesoscale processes in northern South China Sea and Luzon Strait[D]. Qingdao: Graduate University of Chinese Academy of Sciences (Institute of Oceanology, Chinese Academy of Sciences): 131 (in Chinese).
3 闫桐, 齐义泉, 经志友, 2015. 南海上层环流对不同气候态风场响应的数值研究[J]. 热带海洋学报, 34(4): 1-11. YAN TONG, QI YIQUAN, JING ZHIYOU, 2015. A numerical study on the responses of the South China Sea upper circulation to different climatological wind products[J]. Journal of Tropical Oceanography, 34(4): 1-11 (in Chinese).
4 BRUCE J G, 1995. Eddies southwest of the Denmark Strait[J]. Deep Sea Research Part I: Oceanographic Research Papers, 42(1): 13-29.
5 CAPET X, MCWILLIAMS J C, MOLEMAKER M J, et al, 2008a. Mesoscale to submesoscale transition in the California Current System. Part I: Flow structure, eddy flux, and observational tests[J]. Journal of Physical Oceanography, 38(1): 29-43.
6 CAPET X, MCWILLIAMS J C, MOLEMAKER M J, et al, 2008b. Mesoscale to submesoscale transition in the California Current System. Part II: Frontal processes[J]. Journal of Physical Oceanography, 38(1): 44-64.
7 CAPET X, MCWILLIAMS J C, MOLEMAKER M J, et al, 2008c. Mesoscale to submesoscale transition in the California current system. Part III: Energy balance and flux[J]. Journal of Physical Oceanography, 38(10): 2256-2269.
8 CHEN J, 1983. Some explanations for the real-time distribution of sea surface temperature in the northern South China Sea winter[J]. Acta Oceanologica Sinica, 5(3): 391-395.
9 CHU P C, FAN CHENWU, LOZANO C J, et al, 1998. An airborne expendable bathythermograph survey of the South China Sea, May 1995[J]. Journal of Geophysical Research: Oceans (1978-2012), 103(C10): 21637-21652.
10 D’ASARO E, LEE C, RAINVILLE L, et al, 2011. Enhanced turbulence and energy dissipation at ocean fronts[J]. Science, 332(6027): 318-322.
11 DONG CHANGMING, MCWILLIAMS J C, SHCHEPETKIN A F, 2007. Island wakes in deep water[J]. Journal of Physical Oceanography, 37(4): 962-981.
12 FLAMENT P, ARMI L, WASHBURN L, 1985. The evolving structure of an upwelling filament[J]. Journal of Geophysical Research: Oceans, 90(C6): 11765-11778.
13 HAINE T W N, MARSHALL J, 1998. Gravitational, symmetric, and baroclinic instability of the ocean mixed layer[J]. Journal of Physical Oceanography, 28(4): 634-658.
14 HOLMES R M, THOMAS L N, THOMPSON L, et al, 2014. Potential vorticity dynamics of tropical instability vortices[J]. Journal of Physical Oceanography, 44(3): 995-1011.
15 HOSKINS B J, 1974. The role of potential vorticity in symmetric stability and instability[J]. Quarterly Journal of the Royal Meteorological Society, 100(425): 480-482.
16 HOSKINS B J, 1982. The mathematical theory of frontogenesis[J]. Annual Review of Fluid Mechanics, 14(1): 131-151.
17 HU JIANGYU, KAWAMURA H, HONG HUASHENG, et al, 2000. A review on the currents in the South China Sea: Seasonal circulation, South China Sea Warm Current and Kuroshio intrusion[J]. Journal of Oceanography, 56(6): 607-624.
18 HU J Y, KAWAMURA H, TANG D L, 2003. Tidal front around the Hainan Island, northwest of the South China Sea[J]. Journal of Geophysical Research Oceans, 108(C11): 3342.
19 JING ZHIYOU, QI YIQUAN, DU YAN, et al, 2015. Summer upwelling and thermal fronts in the northwestern South China Sea: Observational analysis of two mesoscale mapping surveys[J]. Journal of Geophysical Research: Oceans, 120(3): 1993-2006.
20 KLEIN P, LAPEYRE G, 2009. The oceanic vertical pump induced by mesoscale and submesoscale turbulence[J]. Annual Review of Marine Science, 1: 351-375.
21 LEMARIÉ F, KURIAN J, SHCHEPETKIN A F, et al, 2012. Are there inescapable issues prohibiting the use of terrain- following coordinates in climate models?[J]. Ocean Modelling, 42: 57-79.
22 LÉVY M, KLEIN P, TREGUIER A M, 2001. Impact of sub-mesoscale physics on production and subduction of phytoplankton in an oligotrophic regime[J]. Journal of Marine Research, 59(4): 535-565.
23 LI LI, GUO XIAOGANG, WU RISHENG, 2000. Oceanic fronts in southern Taiwan Strait[J]. Journal of Oceanography in Taiwan Strait, 19(2): 145-156.
24 LIU SUMEI, GUO XINYU, CHEN QI, et al, 2010. Nutrient dynamics in the winter thermohaline frontal zone of the northern shelf region of the South China Sea[J]. Journal of Geophysical Research, 115(C11): C11020.
25 LIU F, TANG S, CHEN C, 2015. Satellite observations of the small-scale cyclonic eddies in the western South China Sea[J]. Biogeosciences, 12(2): 299-305.
26 MARCHESIELLO P, CAPET X, MENKES C, et al, 2011. Submesoscale dynamics in tropical instability waves[J]. Ocean Modelling, 39(1/2): 31-46.
27 MCGILLICUDDY D J, ANDERSON L A, DONEY S C, et al, 2003. Eddy-driven sources and sinks of nutrients in the upper ocean: Results from a 0.1° resolution model of the North Atlantic[J]. Global Biogeochemical Cycles, 17(2): 1035.
28 MCGILLICUDDY D J JR, ANDERSON L A, BATES N R, et al, 2007. Eddy/wind interactions stimulate extraordinary mid-ocean plankton blooms[J]. Science, 316(5827): 1021-1026.
29 MCWILLIAMS J C, 2010. A perspective on submesoscale geophysical turbulence[C]//IUTAM Symposium on Turbulence in the Atmosphere and Oceans. Dordrecht, Netherlands: Springer, 28: 131-141.
30 MUNK W, ARMI L, FISCHER K, et al, 2000. Spirals on the sea[J]. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 456(1997): 1217-1280.
31 PI QINGLING, HU JIANYU, 2010. Analysis of sea surface temperature fronts in the Taiwan Strait and its adjacent area using an advanced edge detection method[J]. Science China Earth Science, 53(7): 1008-1016.
32 QU TANGDONG, MITSUDERA H, YAMAGATA T, 2000. Intrusion of the North Pacific waters into the South China Sea[J]. Journal of Geophysical Research: Oceans (1978-2012), 105(C3): 6415-6424.
33 SHAW P T, CHAO S Y, FU L L, 1999. Sea surface height variations in the South China Sea from satellite altimetry[J]. Oceanologica Acta, 22(1): 1-17.
34 SHCHEPETKIN A F, MCWILLIAMS J C, 2005. The regional oceanic modeling system (ROMS): A split-explicit, free- surface, topography-following-coordinate oceanic model[J]. Ocean Modelling, 9(4): 347-404.
35 STONE P H, 1966. On non-geostrophic baroclinic stability[J]. Journal of the Atmospheric Sciences, 23(4): 390-400.
36 SU JILAN, 2004. Overview of the South China Sea circulation and its influence on the coastal physical oceanography outside the Pearl River Estuary[J]. Continental Shelf Research, 24(16): 1745-1760.
37 TANDON A, GARRETT C, 1994. Mixed layer restratification due to a horizontal density gradient[J]. Journal of Physical Oceanography, 24(6): 1419-1424.
38 TAYLOR J R, FERRARI R, 2011. Ocean fronts trigger high latitude phytoplankton blooms[J]. Geophysical Research Letters, 38: L23601.
39 THOMAS L N, RHINES P B, 2002. Nonlinear stratified spin-up[J]. Journal of Fluid Mechanics, 473: 211-244.
40 THOMAS L N, TANDON A, MAHADEVAN A, 2008. Submesoscale processes and dynamics[M]//HECHT M W, HASUMI H. Ocean modeling in an eddying regime, geophysical monograph series, 177. Washington: American Geophysical Union: 17-38.
41 THOMAS L N, TAYLOR J R, 2010. Reduction of the usable wind-work on the general circulation by forced symmetric instability[J]. Geophysical Research Letters, 37(18): L18606.
42 THOMAS L N, TAYLOR J R, FERRARI R, et al, 2013. Symmetric instability in the Gulf Stream[J]. Deep Sea Research Part II: Topical Studies in Oceanography, 91: 96-110.
43 WANG DONGXIAO, LIU YUN, QI YIQUAN, et al, 2001. Seasonal variability of thermal fronts in the northern South China Sea from satellite data[J]. Geophysical Research Letters, 28(20): 3963-3966.
44 WANG GUIHUA, SU JILAN, CHU P C, 2003. Mesoscale eddies in the South China Sea observed with altimeter data[J]. Geophysical Research Letters, 30(21): OCE 6-1.
45 WANG GUIHUA, LI JIAXUN, WANG CHUNZAI, et al, 2012. Interactions among the winter monsoon, ocean eddy and ocean thermal front in the South China Sea[J]. Journal of Geophysical Research Oceans, 117(C8): C08002.
Outlines

/